Life Under Ice Does Not Take a Winter Break


Roughly 50 million lakes freeze seasonally; it has always been understood that life under the cover of ice takes the winter season off. Sea-ice studies, however, have found that life under the ice, contrary to old beliefs, is very much active.

Previous researches studied the conditions of lakes in summer, but little is known about what happens under the icy cover of winter. With that, Stephanie Hampton, Director of the Center for Environmental Research at Washington University, began to collect and analyze data for the lake conditions in winter, which could then be compared to those in summer.

Hampton’s team first reviewed existing research of under-ice and summer observations conducted between the years 1940 and 2015 from 100 lakes. The findings varied from one lake to another, based on the type of the ice cover and the level of Sun penetration. They have discovered that lakes do not sleep when covered with ice, but rather start a process of food formation for organisms to use during the summer season. Even with the winter’s low temperatures, which slow life down, algae and zooplankton are still abundant, creating food sources for fish and other aquatic creatures after winter.

While studying Lake Baikal in Siberia, Russian researchers have discovered a microecosystem; much of the ice can provide habitat for microorganisms. This microecosystem can vary according to the clearness of the ice. Winter algae blooms are larger than summer blooms, especially when the ice is clear as it provides enough light for the algae that dominates the big winter blooms. However, thicker ice and snow blocks out the Sun and hinders growth. These findings show how winter is necessary for a healthy environment all year round.

As global temperatures rise, how will lake ecosystems respond? As they warm, will lakes—which make up only 3% of the landscape, but bury more carbon than the world’s oceans combined—release more of the greenhouse gases carbon dioxide and methane?

Global warming poses many threats on the whole fresh water system. It adds to the stress of the lake system that is already struggling with aquatic invasive species, deleterious land use changes, nonpoint source pollution, toxic chemical contamination, and coastal habitat degradation/wetlands loss. Potential global warming impacts include reduced water levels, due in particular to decreased winter ice cover allowing more evaporation and warmer water temperatures.

The largest of the Great Lakes of North America, Lake Superior, for example, has increased water temperatures and an earlier onset of summer stratification by about two weeks in just the past 30 years. Within another 30 years, Lake Superior may be mostly ice-free in a typical winter. The water levels of Lake Erie, the fourth largest lake of the five Great Lakes, already below average, could drop 36.5 to45.7 cm by the end of this century, significantly altering shoreline habitat.

Global warming could change internal water cycling in the Great Lakes with longer summers potentially leading to larger Dead Zones—low oxygen content—that could be problematic for the growth of algae, zooplankton, and other microorganisms. The Great Lakes, for instance, which constitute one-fifth of the world’s fresh surface water, are warming at rates faster than the world’s oceans. This will also stimulate blooms of harmful algae in the lakes, leading to toxic cyanobacteria. Other potential consequences include less habitat for coldwater fish, more suitable temperatures for aquatic invasive species and hazardous algal blooms, and more mobilization of contaminated sediments as well as nutrients and toxic chemicals from urban and agricultural runoff.

Scientists also know that freshwater temperatures are rising because warm-water species are moving into areas that were previously too cold, while cool and cold-water species are likewise on the move. Studies are currently conducted in an attempt to alter the rapid climate changes in the lakes around the world because of the global warming effects. These studies will take a long time to try to control all the factors going into this increasingly fast change.

The consequences of the ice melting are incredibly hazardous to the source of livelihood for people who live around those lakes, as well as animals, which would be forced to abandon their natural habitats.


The article was first published in print in SCIplanetEarth Sciences (Spring 2017)

Cover image by wirestock on Freepik

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